document.write( "Question 860723: given a1=94 the common difference is -3, find n so that sn=805. (hint: you will use -b square root b squared -4ac divided by 2a to solve for n) \n" ); document.write( "

Algebra.Com's Answer #518658 by richwmiller(17219) $\"\"$ $\"About$

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S = ½(2a + (n-1)d)n
\n" ); document.write( "805 = ½(2*94 + (n-1)(-3))n
\n" ); document.write( "805 = (191 n)/2-(3 n^2)/2
\n" ); document.write( "n = 10
\n" ); document.write( "n = 161/3
\n" ); document.write( "n must be a whole number.
\n" ); document.write( "so n=10 \n" ); document.write( "

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